1. Field of the Invention
The present invention relates to an ink jet recording head and an ink jet recording apparatus. More particularly, the invention relates to an ink jet head provided with a ceiling plate and a substrate, which is structured by a plurality of ink flow paths and a common liquid chamber communicated with ink discharge ports by bonding the ceiling plate and the substrate together in order to discharge ink by means of discharge energy generating elements for the execution of recording. The invention also relates to an ink jet recording apparatus formed with such ink jet recording head.
2. Related Background Art
The ink jet recording method is such that when recording is executed, ink droplets are allowed to fly from fine discharge ports which are provided for an ink jet head. Then, with the ink droplets thus impacted on a recording medium, a desired recording is performed.
Conventionally, for a recording apparatus that records on paper sheets, cloths, plastic sheets, and OHP sheets, among some others, there have been proposed various recording methods, such as wire-dot method, thermosensitive recording method, heat transfer method, and a recording apparatus having an ink jet head using the ink jet method mounted thereon. Among such methods, the recording apparatus that uses the ink jet method (that is, the ink jet apparatus) is utilized as output means provided for an information processing system, such as a copying machine, a facsimile equipment, an electronic typewriter, a word processor, or as a printer serving as the output terminal of a work station or a handy or portable printer provided for a personal computer, a host computer, a disk device, a video equipment, or the like. Such recording apparatus has been merchandized and put on the market widely.
As the discharge energy generating element that generates energy for discharging ink from the discharge ports of the ink jet head of the ink jet apparatus, there is the one that utilizes electromechanical transducing devices such as piezo-elements. There is also the one that generates heat by the irradiation of electromagnetic wave in order to discharge ink droplets by the thermal action thus arranged, or the one that discharges ink droplets by heating liquid using electrothermal transducing elements provided with heating resistors, among some others.
Also, for the ink jet apparatuses that have been developed in the recent years, it is required to output color images along with the advancement of software and computer technologies. To cope with such situations, the ink jet heads are also made capable of dealing with color images. In addition to such color imaging requirement as this, ink jet recording is required to output color images in higher precision. Therefore, it is attempted to implement making images in higher precision and higher quality with the provision of higher print density, as well as by changing the densities of ink more suitably.
Now, for the ink jet method that discharges ink droplets by heating liquid with the heating resistors, it is generally practiced to use silicon for the formation of the substrate having discharge energy generating elements (such as electrothermal transducing elements) provided therefor.
Then, the ink jet recording head is formed to discharge ink by use of the discharge energy generating elements for the execution of recording in such a manner that the aforesaid substrate is bonded to the ceiling plate, which is provided with grooves that become a plurality of ink flow paths communicated with a plurality of ink discharge ports, and also, provided with a recessed portion that becomes the common liquid chamber communicated with the ink flow paths, for the formation of these ink flow paths and the common liquid chamber. For the conventional ink jet recording head thus formed, the silicon substrate having the discharge energy generating elements arranged therefor to discharge ink is die bonded directly to the aluminum base plate substrate which is standardized for the provision of a head.
When the die bonding is executed, a bonding agent 22 such as silver paste, which has a good heat conductivity, is used so that the heat of the silicon substrate which becomes higher due to the generation of the thermal energy is radiated by transferring it to the aluminum base plate substrate quickly. In this way, it is arranged to eliminate the accumulation of intense heat in the silicon substrate, hence making it possible to obtain good prints even at a printing of higher frequency.
However, if the aforesaid ink jet recording head a is formed with a substrate having a printing width of more than one inch, at the same time, the recording density (the arrangement density of the discharge energy generating elements) thereof being made 600 dpi or more, a drawback may be encountered that the silicon substrate 20 is warped or cracked due to the strong bonding force exerted by the bonding agent 22 used for the die bonding, because the silicon substrate 20 is die bonded directly to the aluminum base substrate 21 (see FIG. 4). More specifically, in a case where a silicon substrate 20 having the printing width of more than one inch is die bonded to an aluminum base plate substrate 21, the thermal expansion coefficient of the aluminum base plate becomes as extremely great as 2.37.times.10.sup.-5 against that of the silicon substrate which is 0.42.times.10.sup.-5 as shown in FIG. 3. Then, these substrates are bonded usually at a cure temperature of as high as 120.degree. C. to 150.degree. C. approximately. Therefore, the ratio of shrinkage between the silicon substrate 20 and the aluminum base plate substrate 21 is different when returned to the room temperature. Then, as shown in FIG. 4, for example, warping may take place on the substrate 20 in the arrangement direction of the discharge energy generating element. As a result, it becomes difficult to bond the ceiling plate and the substrate in parallel and smoothly in flat. A gap is made on the substrate inevitably between each of the adjacent ink flow paths, hence dispersing the discharge pressure exerted by each of the discharge energy generating elements to the adjacent ink flow paths, respectively. In this manner, the speed of ink discharges becomes instable when recording is made. Also, the accuracy of impact becomes degraded to bring about printing disturbance easily, hence making it difficult to implement recording in higher quality.
On the other hand, if the silicon rubber bonding agent or the like which may absorb the difference in the thermal expansion coefficient between them is used for die bonding in order to avoid the cracking or warping of the silicon substrate, it becomes difficult to radiate heat to the aluminum base plate when the target density is as high as 600 dpi or more. Consequently, the residual heat is inevitably accumulated in the silicon substrate to make it impossible to obtain good prints particularly when printing is made at a high frequency.
Further, for the conventional ink jet recording head, it is arranged to give criteria to the aluminum base plate for assembling a head. Therefore, due to the expansion of aluminum caused by generated heat during printing, the distance between the abutting reference on the carriage and the discharge nozzles tends to be expanded. Hence, a problem is encountered among some others that it becomes difficult to obtain the dot impact position in good accuracy.